1. Field of the Invention
The present invention relates to a zoom lens system for use as an imaging lens system for forming an image onto an imaging device, such as a CCD or CMOS, etc.
2. Description of the Prior Art
In recent years, high quality and fast zoom lens systems having a smaller F-number have been in demand, since further miniaturization of the pixels of imaging devices, such as CCDs and CMOSs, etc., and higher sensitivity of CCDs, have been attained. However, in reality, relatively slow zoom lens systems having an F-number of approximately 2.8 through 3.5 at the short focal length extremity are predominant.
Examples of the above-mentioned conventional zoom lens systems are taught in, e.g., Japanese Unexamined Patent Publication (hereinafter, JUPP) Nos. 2001-318311, 2003-015035, 2005-70696, 2005-70697, Japanese Patent Nos. 3652179 and 3709148, and JUPP No. 2006-126418.
Usually when an F-number becomes smaller, the correcting of spherical aberration and other aberrations becomes extremely difficult. Hence, in order to correct aberrations, the number of lens elements is significantly increased, and the number of lens groups are increased. Consequently, further miniaturization of the zoom lens system substantially becomes impossible.